Laser Doppler Velocimetry is a clinically applicable, non-invasive technique which enables one to obtain measurements of the blood flow rate at discrete sites in the retinal vasculatue accurately and with relative ease. Since the retinal blood flow is a dynamic quantity, its complete characterization requires the capability of measuring instantaneous changes in the velocity of red blood cells flowing in individual retinal vessels. The laser Doppler technique is the only known non-invasive technique with this capability. Central to the functioning of the retinal circulation is its ability to autoregulate its blood flow supply in the presence of physiological stress. A number of major disease processes with specific ocular complications have been linked to a pathological functioning of the autoregulatory mechanism. The specific aims of the proposed research are (a) improve the accuracy of the measurements by appropriate electronic and optical modification of currently available instrumentation; (b) improve the ease with which data may be acquired and analyzed by implementation of techniques which allow stabilization of the incident laser beam on the target vessel; (c) perform basic studies of the autoregulation process by performing laboratory experiments under conditions of imposed physiological stress and under conditions of photocoagulation-induced retinal blood flow alterations; (d) quantitatively characterize the normal human retinal circulation; and (e) quantitatively characterize and determine the effects of therapeutic interventions upon the retinal circulation of patients with diabetic retinopathy, branch vein occlusion, central vein occlusion, systemic hypertension, ocular hypertension, and glaucoma.